Implement SkGifCodec::onSkipScanlines()

src/codec/SkCodec_libgif.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkColorTable.h"
 #include "SkImageInfo.h"
@@ skipping 132 matching lines @@
     /*
      * @return true if the read is successful and false if the read fails.
      */
     bool readRow();
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& opts,
                    SkPMColor inputColorPtr[], int* inputColorCount) override;
 
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
 
+    bool onSkipScanlines(int count) override;
+
+    /*
+     * For a scanline decode of "count" lines, this function indicates how
+     * many of the "count" lines should be skipped until we reach the top of
+     * the image frame and how many of the "count" lines are actually inside
+     * the image frame.
+     *
+     * @param count           The number of scanlines requested.
+     * @param rowsBeforeFrame Output variable.  The number of lines before
+     *                        we reach the top of the image frame.
+     * @param rowsInFrame     Output variable.  The number of lines to decode
+     *                        inside the image frame.
+     */
+    void handleScanlineFrame(int count, int* rowsBeforeFrame, int* rowsInFrame);
+
     SkScanlineOrder onGetScanlineOrder() const override;
 
     /*
      * This function cleans up the gif object after the decode completes
      * It is used in a SkAutoTCallIProc template
      */
     static void CloseGif(GifFileType* gif);
 
     /*
      * Frees any extension data used in the decode
@@ skipping 19 matching lines @@
     SkAutoTDeleteArray<uint8_t>             fSrcBuffer;
     const SkIRect                           fFrameRect;
     const uint32_t                          fTransIndex;
     uint32_t                                fFillIndex;
     const bool                              fFrameIsSubset;
     SkAutoTDelete<SkSwizzler>               fSwizzler;
     SkAutoTUnref<SkColorTable>              fColorTable;
 
     typedef SkCodec INHERITED;
 };